Advanced Analog Technology, Inc.
April 2007
AAT1164/AAT1164B/AAT1164C
Compensator design guide:
Bode Diagram
60
1
2
1. Crossover frequencyfci
2. Gain margin>10dB
<
fS
40
20
0
-20
-40
-90
3. Phase margin>45
-135
-180
-225
-270
4. The LVI(s) = 1 at crossover frequency, Therefore,
the compensator resistance,
R
is determined by:
C
102
103
104
Frequency (Hz)
105
106
R + 2r
VO 2πfciCOUTRCS
L
C
RC
=
Figure 7. Bode Plot of Loop Gain Using Matlab®
Simulation
VFB
gmk
r
1− D R −
)
(
L
1− D
(
)
Table 3. k Factor Table
Best Corner
Positive and Negative LDO Driver
Output Voltage Selection
k Factor
COUT
Frequency
The output voltage of positive LDO driver is set by a
resistive divider from the output (VOUT3) to GND with the
center tap connected to the IN3, where VIN3, the positive
LDO driver feedback regulation voltage, is 1.25V.
21.533µF
25.079µF
32.587µF
36.312µF
38.469µF
23.740kHz
21.842kHz
20.095kHz
15.649kHz
13.247kHz
4.692
5.083
6.042
5.230
4.703
Choose R6 (Figure 8) between 10k
Ω and 51kΩ . And
calculate R5 with the following equation.
5. The output filter capacitor is chosen so
pole cancels R C zero
C R
OUT L
6
VOUT3
R5 = R
−1
C
C
V
IN3
R
L
The output voltage of negative LDO driver is set by a
resistive divider from the output (VOUT2) to VREF with
the center tap connected to IN2, where VIN2, the
negative LDO driver feedback regulation voltage, is
εRCCC = COUT
+ rC , and
2
R
L
COUT
CC
=
+ rC
εRC
2
ε = (1 ~ 3)
0.25V. Choose R9 (Figure 9) between10k
Ω and
51kΩ and calculate R8 with the following equation.
Example 3:
V
= 5V, VO = 13.3V, IO = 300mA, fS = 1,190kHz,
IN
9
V
− VOUT2
IN2
R8 = R
VFB = 1.233V,
L
= 6.65µH, gm = 85µS,
VREF − V
IN2
rL = 76.689mΩ
r
= 9.13mΩ RF = 0.7667Ω , C = 1.95nF,
C
C
µF
R
= 7.6kΩ
,
COUT = 38.5
,
ε
= 3,
R
= 0.23V/A.
C
CS
–
–
–
Advanced Analog Technology, Inc
Version 1.00
. –
Page 19 of 24
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
